The overall objectives of this project are: (1) to obtain a detailed understanding of structure and function of the nervous system of an isogenic organism (Daphnia) by parallel anatomical, physiological and behavioral studies and (2) to study the effects of environmental variability during embryogenesis upon the expression of the constant genetic background at the level of structure and function of the nervous system. We propose to use our technique of computer reconstruction from serial sections in order to build an anatomical map of the Daphnia visual system and its synaptic pathways, from photoreceptors to muscles. The physiological validity of the anatomical map will be tested by observing the uptake of extracellular dye (horse radish peroxidase) into the vesicles of synapses in pathways associated with specific types of photostimulation and related behavioral responses. The invariance of pathways and their functional characteristics will be studied by comparing various specimens from the same clone. Environmental variations during embryogenesis include: (1) destruction of subsets of cells by use of a UV microbeam, (2) centrifugation of pre-mitotic eggs in order to induce abnormal development of the brain, and (3) introduction of anisotropic temperature distributions to produce abnormal growth rates in different regions of the brain. The inherent capacity of our methods to detect small changes in both the structure and function of the nervous system that result in altered behavior can be used to identify and select means, both physical and chemical, by which the genetic control of structure and function can be modified or destroyed. This should further help us to clarify the role and model of action of the genes and of environmental disturbances in the control of macroscopic structure and function.